to keep the radios up you would need to modify the control head interface board.
The head routes power back down the cable and tells the radio to power up. If you switched the head to a different radio the radio would power down.
The other big issue would be the control head updating its display. The head would loose power as it was switched so it would also cause the radio to reset.
the busy lines would also cause confusion is a 4 position switch configuration.
I will say this, it CAN"T be done with a 9 series head, as it's smart and contains the channel information.
Part of the advanced firmware is the command set that see's the head swap and holds the radio in place and doesn't change the radio status of cause a reset.
My guess is that you would get one radio to work and the other 3 would fail on power up and as soon as you switched to another radio the first radio would get an 01/90 error. All in all, I would say that you either do it with the correct Motorola parts or don't do it at all.
Another option is this. The mw800 or mw810 had a software package on it that was called vRCH or virtural Remote Control Head. It ran on a computer and interfaced to the radios via a mini-RIB. It would send basic commands to the radio (which required a control head to be connected) and would change volume, channel and zone. It had a bit more functionality than that, but not alot. You still needed a mike for each radio but the heads could be stowed or mounted under the MDT (laptop dock) and never touched unless the MDT was non functional.
A third option is an NCS-250 patch box. I put one of these in a fire chiefs vehicle with 4 radios, 3 were trunked. It took installing some time delay boxes to get the audio to all come through because of the trunking talk permit tone delay, but it's a functional solution. It uses a select and unselect speaker and a single mike. It works like a dispatch console giving the user the ability to patch two or more radios together, talk on multiple channels and/or talk groups at the same time and even patch the receive audio over to the external siren PA system if one desires. Google NSC-250 for the skinny on it. It's not a cure all, but if you are wanting to clean up an install, add functionality to it to boot, couple the vRCH with the NCS-250 and all the other radio grreks will crown you king of the hill and want one too.
What more can I say